If you are using EstateExec, it will calculate task due dates for you once you enter the decedent's date of death in the Decedent tab, and you can get more details about an individual task by clicking on it in the Tasks tab.
General tasks can be grouped into the following time periods (click a link for details):
There will also likely be a number of additional actions you need to take in the course of managing the estate, that are independent of the decedent's death, and just need to be handled as they arise (e.g., filing any annual property taxes, paying small business license fees, renewing property insurance policies, maintaining household property, paying utility bills, etc.).
You can visualize the overall executor process as follows: